Process of preparing, grinding, or polishing tools



Patented July 31, 1934 rao'onss or PREPARING, GRINDING, on

POLISHING TOOLS Ernst Elbel and Otto Sussenguth, Erkner, near Berlin, Germany, assignors to Bakelite Gesellschaft mit beschrankter Haftung, Berlin, Germany No Drawing. Application February 21, 1931,

fegaal No. 517,632. In Germany February 28, 9

2 Claims. 1 (Cl. 51-278) It is well known in the art to produce grinding gendering resins such as a phenol and formaldeor polishing tools from granular abrasive matehyde and react them in the presence of a resitole rials byusing phenol-aldehyde 'resins'as binders. solvent as set out in application 497,063. A few According to the known art, the procedure is to of the solvents that can be used are hydrogenated mix the abrasive material with the hardenable phenols,,such as hexalin, methyl-hexalin, hexaw phenol resin or phenol resin composition, and hydro-betanaphthol. Various liquids, such as then to mold into the desired 'form, as, for intetralin, or brombenzol, even though they do not stance, into grinding wheels, by simultaneous dissolve resitoles, can also be added to the solapplication of heat and pressure. However, it vents. Such other solvents can be used as do w is also possible to proceed in such a way that not dissolve the B resin at normal pressure, but the phenol resin, either molten or mixed with will dissolve the B resin when heated under presdiluents or plasticizers and after the admixture sure, such as, for example, a mixture of equal of the abrasive, is molded. according to the so-. parts of benzol and methyl alcohol. 1 Other called cold-molding process, either at the normal hardenable or non-hardenable, either natural or 15 or at moderately elevated temperatures. The synthetic resins can'be used along with the resiconversion of the hardonable phenolic resin toles, that is to, say, as a mixture. The solutions binders contained in the molded objects is thereof resitole, or the solutions of resitole containing upon carried out by the application of heat. the abrasives can still be processed when cata- This invention concerns improvements in the lysts, plasticizers, hardeners, etc. are added.

20 known processes. It has been found that the These materials may be added to the mixtures characteristics of grinding and polishing tools at any convenient stage of the preparation. A can be appreciably improved, if solutions of mixture of several B resins or a solution cony resitole resins, thatis to say, solutions of phenol taining several B resins may also be used.

aldehyde resins which are in the so-called B The preparation of grinding and polishing tools state, are used for their production. Granular follow the usual manner of mixing the abrasive 8o abrasive materials can be incorporated in such materials intimately with the resitole resin in aresitole resin solution. 0r, resoles, or a mixsolution and then producing the objects by hotture of a novolak .with hardening agents, can molding or by cold-molding and subsequent bakbe dissolved in a liquid which will dissolve resiing. It is, of course, possible to use any other 30 toles, the abrasives are then mixed in, and the suitable process for preparing the abrasives and mixture 0f abrasive and solution is heated to the the resin binders. The solvent used to dissolve formation of the resitole. Finally, it is also posthe resitole resin may be entirely or partially sible to mix the ingredients of a synthetic resin, driven olf from the mixtures under"- the proper that is, P a y a d ca a yst, Wit the conditions, for example, before the hardening 35 abrasive and a solvent, which will dissolve resoles step, as well as resitoles, and then to carry out the An advantage of this invention lies especially condensation of the resinous components to the in the fact that the grinding and polishing tools resitole stage. Hardeners may also be added in produced from B resin solutions, under otherwise this step. To produce resitole solutions, or resitole similar conditions, exhibit appreciably greater 0 solutions containing the abrasive materials, the mechanical strength than the products made acprocedure described i patent applications cording to the known processes. The explana- 295344 O u 1928, 2, 3 of ua y 2 tion of this improvement lies in the fact that the 1930, and 497,063 of November 20, 1930, can remaining step of conversion of the phenol resin be follow d. Bri y these ppli i n de ribe to the 0 state is considerably facilitated by the 45 the preparati n f resitole solutions. n appl use of resin in the substantially polymerized B cation 295.3 a s e iS incflrporated as state, and that on the other hand, the solutions with a suit v m t r up f ycli coat theparticles of the granular abrasive maketones or equivalent .alcohols, their homologs terial uniformly, so that a, uniform distribution and esters, hydrogenated naphthalenes, etc. In of the binder and, likewise, a uniform cementing- 5 place of resitoles, resoles or A type resins or their together of the individual abrasive particles is equivalents, that is, novolak resins together with insured. Hence it follows that, by using the hardening agents can be used and then carried process of this invention, grinding tools can be to the resitole condition in the solvents; this made whose strength will be appreciably greater forms the subject matter of application 422,683. than of those products made from the identical It is also possible to add the ingredients enbinding mixtures, but according to the processes 'sures.

of the known art. If, on the other hand, grinding tools with lesser strength are desired, it is possible to produce them by following the process of this invention, but cutting down the quantity of resin binder used below the quantity'used in the known processes.

Example 1 8 kilos phenol-aldehyde resin, pulverized, in resole condition, are mixed in a kneading machine with 2 kilos methyl-hexalin and kilos silicon carbide grains by heating for 1 hour to 110 C. The mixture becomes tougher while emitting only slight vapors, and it is heated so long as it may still be formed into a balPby hand when cold.

The mixture is molded by the application of pressure. The pressure depends upon the degree of dryness of the mixture and normally is 300 to 600 kilos per square centimeter surface. Onecan also use considerably lower or higher pres- If the heat is applied at the same time that molding is done, it is advantageous to work at a temperature of about 180- (3.; lower and higher temperatures however can be used. If molding is done without simultaneous application of heat, the molded articles are hardened subsequently at 60 to 180 C. with or without the mold. The hardening process can be started first at lower temperatures and then the temperature raised gradually, or it is possible to subject the molded article from the beginning to a temperature above 100 0.

Example 2 10 kilos cresol, 2.8 kilos hexamethylenetetramine, 3 kilos hexalin and 85 kilos aluminum oxide grains are mixed in the kneading machine and processed until thecondition is reached as described in Example 1.

Condensation products of phenols and formaldehyde (or substances forming formaldehyde), whose polymerization has proceeded to the point where they no longer melt on heating, but only soften, have been considered as B resins or resitoles for the purpose of -this invention. These products were formerly regarded as insoluble. As a matter of fact they are insoluble in the usual solvents for phenol-aldehyde resins, such as alcohol, but ashas been pointed out, they may be dissolved in certain specific liquids, or mixtures of liquids, at normal or elevated pressure, and may be processed into objects having very valuable properties.

The term hardenable resins as used in the present application is understood to include all those resin-like products which can be prepared in a soluble and fusible condition and, if sufficiently heated, transformed into a hard, insoluble and infusible condition. Such hardenable resins are for example the condensati m products from the various phenols and aldehydes,' o r aldehydeyielding bodies, as well as the mixtures of novolaks with hardening agents; also condensation products from urea and aldehydes; from polyvalent alcohols and polybasic acids, etc, As fillers we not only include the usual fillers, but also other additions to hardenable synthetic resins customary in'the art, for example, plasticizing agents, fire-proofing material, non-hardenable synthetic or natural resins, or the like. Therefore the invention is not limited to the specific substances or steps or proportions stated in the examples, but it relates generally to the manufacture of grinding or polishing tools, and moldable compositions suitable for their manu- 'facture' aswell'as other products coming within its scope as set out in the following claims.

The following definitions are intended for the terms resole, resitole, and novolak. A resole is a resin of the type hardenable by heat to a final infusible and insoluble condition but reacted only to the stage where it still melts when heated and is soluble in acetone; this is also known as the A stage. A resitole is a resin of the same type as a resole but further-reacted to a-B stage where it has become infusible, i. e., it' does not melt though it softens decidedly on heating, and is insoluble but swells in acetone. A novolak is a distinctly different type of resinous reaction 305 product in that practically speaking it does not harden upon heating to an infusible insoluble condition but remains soluble and fusible. The

resins here defined are those made from phenols or their homologs and derivatives with and methylene or aldehyde agent as is well understood by those skilled in the art.

fishing implements which comprises mixing a heat-hardenable phenol-aldehyde resin in 50111- 05 tion of a solvent selected from the group of hydrogenated aromatic hydrocarbons, hexahydrogenated phenols and their esters and hydroaromat'ic ketones with an abrasive filler, heating the mixture to transform the resin to the resitole 'state, molding the mixture and hardening the resin by heating.

ERNST ELBEL. OTTO SUSSENGU'I'H. 

